Impact of Angular Distortion on the Fatigue Performance of High-Strength Steel T-Joints in as-Welded and High Frequency Mechanical Impact-Treated Condition

Abstract

In general, distortion has significant effects on the assembly process of welded structures and remarkable influences on the strength of the welds. Therefore, this work focuses on the effect of angular welding distortion on fatigue strength to improve transferability of specimen results to components. Experimental investigations cover manufacturing and fatigue testing of three single-sided transversal stiffeners series exhibiting different angular distortions. The fatigue test results of as-welded specimen show a distinct link between fatigue performance and initial angular distortion. However, in case of a high frequency mechanical impact (HFMI)-treated weld toe, the fatigue strength increases up to base material level and is independent of the distortion. A comprehensive numerical analysis reveals a complex interaction between the applied nominal load, initial specimen distortion and the local stress field. In this context, an engineering-feasible assessment is derived to estimate the local effective stresses featuring the acting local stress range as well as the stress ratio. The application of this distortion factor enables the setup of a uniform S/N-curve with a significantly reduced scatter band.

Analysis of fatigue notch effect due to axial misalignment for ultra high-strength steel butt joints

“…This method assumes a very high stiffness of the rest rig compared with the specimen, otherwise the influence of the specimens secondary bending is not assessed properly. In [27], a holistic study on the effect of secondary bending including a strain gauge measurements and subsequent comparison to numerical results was performed using specimens of similar stiffness and the same testing facilities. The investigations show the use of rigid clamping is sufficient for the present test rig and specimen combination.…”

Parametric Formulae for Elastic Stress Concentration Factor at the Weld Toe of Distorted Butt-Welded Joints

“…Hence, a two-step FE analysis with the same material and mesh parameters as undistorted butt-welded joints (see Section 2.2.1) is carried out for distorted joints under fatigue test conditions, as illustrated in Figure 5. In detail, the left clamping area is fully fixed corresponding to a specimen gripped on one side [27]. In the first step, hydraulic grips, which are modelled with rigid bodies, straighten the distorted joints on the other side.…”

“…Only a few studies have considered the SCF (K act ) under fatigue test conditions. Ottersbock et al [27] recently proposed a formula to describe the functional relationship between the actual SCF K act of distorted T-shape joints and distortion angle α, tensile loading σ nom . The formula mainly contributes to the hot-spot stress approach and the effective notch stress approach, both of which use the simplified profile of weld bead (e.g., the effective notch stress approach assumes 1.0 mm toe radius with 45 • flank angle for the welds of T-shape joints).…”

“…To the best of our knowledge, there are no solutions available in the literature to estimate the clamping stress σ clamp at the weld toe of butt joints. Although Ottersbock et al [27] have proposed a set of formulae to evaluate the σ clamp of distorted T-shape joints in terms of nominal stress, hot-spot stress and notch stress, these formulae mainly contribute to clarify the linear relationship between σ clamp and α. Only distortion angle α was considered as the independent variable in the formulae.…”

“…Only a few concerned studies can be found currently in the literature. For example, analytical and experimental research on the SCF of joints with angular distortion was carried out by Xing and Dong [26] and Ottersbock et al [27] for cruciform joints and T-shape joints, respectively. To our best knowledge, there are no available wide-spread solutions for the SCF and clamping-induced stress of distorted butt-welded joints under fatigue test conditions.…”